1 /*
2 * Copyright (c) 2005, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "logging/log.hpp"
27 #include "memory/resourceArea.hpp"
28 #include "oops/klass.inline.hpp"
29 #include "oops/markOop.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/atomic.hpp"
32 #include "runtime/basicLock.hpp"
33 #include "runtime/biasedLocking.hpp"
34 #include "runtime/task.hpp"
35 #include "runtime/threadSMR.hpp"
36 #include "runtime/vframe.hpp"
37 #include "runtime/vmThread.hpp"
38 #include "runtime/vm_operations.hpp"
39 #include "trace/tracing.hpp"
40
41 static bool _biased_locking_enabled = false;
42 BiasedLockingCounters BiasedLocking::_counters;
43
44 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
45 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
46
47 static void enable_biased_locking(InstanceKlass* k) {
48 k->set_prototype_header(markOopDesc::biased_locking_prototype());
49 }
50
51 class VM_EnableBiasedLocking: public VM_Operation {
52 private:
53 bool _is_cheap_allocated;
54 public:
55 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
56 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
57 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
58 bool is_cheap_allocated() const { return _is_cheap_allocated; }
59
60 void doit() {
61 // Iterate the class loader data dictionaries enabling biased locking for all
62 // currently loaded classes.
63 ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking);
64 // Indicate that future instances should enable it as well
65 _biased_locking_enabled = true;
66
67 log_info(biasedlocking)("Biased locking enabled");
68 }
69
70 bool allow_nested_vm_operations() const { return false; }
71 };
72
73
74 // One-shot PeriodicTask subclass for enabling biased locking
75 class EnableBiasedLockingTask : public PeriodicTask {
76 public:
77 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
78
79 virtual void task() {
80 // Use async VM operation to avoid blocking the Watcher thread.
81 // VM Thread will free C heap storage.
82 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true);
83 VMThread::execute(op);
84
85 // Reclaim our storage and disenroll ourself
86 delete this;
87 }
88 };
89
90
91 void BiasedLocking::init() {
92 // If biased locking is enabled, schedule a task to fire a few
93 // seconds into the run which turns on biased locking for all
94 // currently loaded classes as well as future ones. This is a
95 // workaround for startup time regressions due to a large number of
96 // safepoints being taken during VM startup for bias revocation.
97 // Ideally we would have a lower cost for individual bias revocation
98 // and not need a mechanism like this.
99 if (UseBiasedLocking) {
100 if (BiasedLockingStartupDelay > 0) {
101 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
102 task->enroll();
103 } else {
104 VM_EnableBiasedLocking op(false);
105 VMThread::execute(&op);
106 }
107 }
108 }
109
110
111 bool BiasedLocking::enabled() {
112 return _biased_locking_enabled;
113 }
114
115 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
116 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
117 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
118 if (info != NULL) {
119 return info;
120 }
121
122 info = new GrowableArray<MonitorInfo*>();
123
124 // It's possible for the thread to not have any Java frames on it,
125 // i.e., if it's the main thread and it's already returned from main()
126 if (thread->has_last_Java_frame()) {
127 RegisterMap rm(thread);
128 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
129 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
130 if (monitors != NULL) {
131 int len = monitors->length();
132 // Walk monitors youngest to oldest
133 for (int i = len - 1; i >= 0; i--) {
134 MonitorInfo* mon_info = monitors->at(i);
135 if (mon_info->eliminated()) continue;
136 oop owner = mon_info->owner();
137 if (owner != NULL) {
138 info->append(mon_info);
139 }
140 }
141 }
142 }
143 }
144
145 thread->set_cached_monitor_info(info);
146 return info;
147 }
148
149 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
150 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
151 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
152 markOop mark = obj->mark();
153 if (!mark->has_bias_pattern()) {
154 if (log_is_enabled(Info, biasedlocking)) {
155 ResourceMark rm;
156 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT
157 ", mark " INTPTR_FORMAT ", type %s"
158 ", requesting thread " INTPTR_FORMAT
159 " because it's no longer biased)",
160 p2i((void *)obj), (intptr_t) mark,
161 obj->klass()->external_name(),
162 (intptr_t) requesting_thread);
163 }
164 return BiasedLocking::NOT_BIASED;
165 }
166
167 uint age = mark->age();
168 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
169 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
170
171 // Log at "info" level if not bulk, else "trace" level
172 if (!is_bulk) {
173 ResourceMark rm;
174 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
175 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
176 ", allow rebias %d, requesting thread " INTPTR_FORMAT,
177 p2i((void *)obj),
178 (intptr_t) mark,
179 obj->klass()->external_name(),
180 (intptr_t) obj->klass()->prototype_header(),
181 (allow_rebias ? 1 : 0),
182 (intptr_t) requesting_thread);
183 } else {
184 ResourceMark rm;
185 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
186 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
187 " , allow rebias %d , requesting thread " INTPTR_FORMAT,
188 p2i((void *)obj),
189 (intptr_t) mark,
190 obj->klass()->external_name(),
191 (intptr_t) obj->klass()->prototype_header(),
192 (allow_rebias ? 1 : 0),
193 (intptr_t) requesting_thread);
194 }
195
196 JavaThread* biased_thread = mark->biased_locker();
197 if (biased_thread == NULL) {
198 // Object is anonymously biased. We can get here if, for
199 // example, we revoke the bias due to an identity hash code
200 // being computed for an object.
201 if (!allow_rebias) {
202 obj->set_mark(unbiased_prototype);
203 }
204 // Log at "info" level if not bulk, else "trace" level
205 if (!is_bulk) {
206 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
207 } else {
208 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
209 }
210 return BiasedLocking::BIAS_REVOKED;
211 }
212
213 // Handle case where the thread toward which the object was biased has exited
214 bool thread_is_alive = false;
215 if (requesting_thread == biased_thread) {
216 thread_is_alive = true;
217 } else {
218 ThreadsListHandle tlh;
219 thread_is_alive = tlh.includes(biased_thread);
220 }
221 if (!thread_is_alive) {
222 if (allow_rebias) {
223 obj->set_mark(biased_prototype);
224 } else {
225 obj->set_mark(unbiased_prototype);
226 }
227 // Log at "info" level if not bulk, else "trace" level
228 if (!is_bulk) {
229 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread ("
230 PTR_FORMAT ")", p2i(biased_thread));
231 } else {
232 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
233 PTR_FORMAT ")", p2i(biased_thread));
234 }
235 return BiasedLocking::BIAS_REVOKED;
236 }
237
238 // Log at "info" level if not bulk, else "trace" level
239 if (!is_bulk) {
240 log_info(biasedlocking)(" Revoked bias of object biased toward live thread ("
241 PTR_FORMAT ")", p2i(biased_thread));
242 } else {
243 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread ("
244 PTR_FORMAT ")", p2i(biased_thread));
245 }
246
247 // Thread owning bias is alive.
248 // Check to see whether it currently owns the lock and, if so,
249 // write down the needed displaced headers to the thread's stack.
250 // Otherwise, restore the object's header either to the unlocked
251 // or unbiased state.
252 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
253 BasicLock* highest_lock = NULL;
254 for (int i = 0; i < cached_monitor_info->length(); i++) {
255 MonitorInfo* mon_info = cached_monitor_info->at(i);
256 if (mon_info->owner() == obj) {
257 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
258 p2i((void *) mon_info->owner()),
259 p2i((void *) obj));
260 // Assume recursive case and fix up highest lock later
261 markOop mark = markOopDesc::encode((BasicLock*) NULL);
262 highest_lock = mon_info->lock();
263 highest_lock->set_displaced_header(mark);
264 } else {
265 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
266 p2i((void *) mon_info->owner()),
267 p2i((void *) obj));
268 }
269 }
270 if (highest_lock != NULL) {
271 // Fix up highest lock to contain displaced header and point
272 // object at it
273 highest_lock->set_displaced_header(unbiased_prototype);
274 // Reset object header to point to displaced mark.
275 // Must release storing the lock address for platforms without TSO
276 // ordering (e.g. ppc).
277 obj->release_set_mark(markOopDesc::encode(highest_lock));
278 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
279 // Log at "info" level if not bulk, else "trace" level
280 if (!is_bulk) {
281 log_info(biasedlocking)(" Revoked bias of currently-locked object");
282 } else {
283 log_trace(biasedlocking)(" Revoked bias of currently-locked object");
284 }
285 } else {
286 // Log at "info" level if not bulk, else "trace" level
287 if (!is_bulk) {
288 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
289 } else {
290 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
291 }
292 if (allow_rebias) {
293 obj->set_mark(biased_prototype);
294 } else {
295 // Store the unlocked value into the object's header.
296 obj->set_mark(unbiased_prototype);
297 }
298 }
299
300 // If requested, return information on which thread held the bias
301 if (biased_locker != NULL) {
302 *biased_locker = biased_thread;
303 }
304
305 return BiasedLocking::BIAS_REVOKED;
306 }
307
308
309 enum HeuristicsResult {
310 HR_NOT_BIASED = 1,
311 HR_SINGLE_REVOKE = 2,
312 HR_BULK_REBIAS = 3,
313 HR_BULK_REVOKE = 4
314 };
315
316
317 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
318 markOop mark = o->mark();
319 if (!mark->has_bias_pattern()) {
320 return HR_NOT_BIASED;
321 }
322
323 // Heuristics to attempt to throttle the number of revocations.
324 // Stages:
325 // 1. Revoke the biases of all objects in the heap of this type,
326 // but allow rebiasing of those objects if unlocked.
327 // 2. Revoke the biases of all objects in the heap of this type
328 // and don't allow rebiasing of these objects. Disable
329 // allocation of objects of that type with the bias bit set.
330 Klass* k = o->klass();
331 jlong cur_time = os::javaTimeMillis();
332 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
333 int revocation_count = k->biased_lock_revocation_count();
334 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
335 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
336 (last_bulk_revocation_time != 0) &&
337 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
338 // This is the first revocation we've seen in a while of an
339 // object of this type since the last time we performed a bulk
340 // rebiasing operation. The application is allocating objects in
341 // bulk which are biased toward a thread and then handing them
342 // off to another thread. We can cope with this allocation
343 // pattern via the bulk rebiasing mechanism so we reset the
344 // klass's revocation count rather than allow it to increase
345 // monotonically. If we see the need to perform another bulk
346 // rebias operation later, we will, and if subsequently we see
347 // many more revocation operations in a short period of time we
348 // will completely disable biasing for this type.
349 k->set_biased_lock_revocation_count(0);
350 revocation_count = 0;
351 }
352
353 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
354 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
355 revocation_count = k->atomic_incr_biased_lock_revocation_count();
356 }
357
358 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
359 return HR_BULK_REVOKE;
360 }
361
362 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
363 return HR_BULK_REBIAS;
364 }
365
366 return HR_SINGLE_REVOKE;
367 }
368
369
370 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
371 bool bulk_rebias,
372 bool attempt_rebias_of_object,
373 JavaThread* requesting_thread) {
374 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
375
376 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
377 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
378 (bulk_rebias ? "rebias" : "revoke"),
379 p2i((void *) o),
380 (intptr_t) o->mark(),
381 o->klass()->external_name());
382
383 jlong cur_time = os::javaTimeMillis();
384 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
385
386
387 Klass* k_o = o->klass();
388 Klass* klass = k_o;
389
390 {
391 JavaThreadIteratorWithHandle jtiwh;
392
393 if (bulk_rebias) {
394 // Use the epoch in the klass of the object to implicitly revoke
395 // all biases of objects of this data type and force them to be
396 // reacquired. However, we also need to walk the stacks of all
397 // threads and update the headers of lightweight locked objects
398 // with biases to have the current epoch.
399
400 // If the prototype header doesn't have the bias pattern, don't
401 // try to update the epoch -- assume another VM operation came in
402 // and reset the header to the unbiased state, which will
403 // implicitly cause all existing biases to be revoked
404 if (klass->prototype_header()->has_bias_pattern()) {
405 int prev_epoch = klass->prototype_header()->bias_epoch();
406 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
407 int cur_epoch = klass->prototype_header()->bias_epoch();
408
409 // Now walk all threads' stacks and adjust epochs of any biased
410 // and locked objects of this data type we encounter
411 for (; JavaThread *thr = jtiwh.next(); ) {
412 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
413 for (int i = 0; i < cached_monitor_info->length(); i++) {
414 MonitorInfo* mon_info = cached_monitor_info->at(i);
415 oop owner = mon_info->owner();
416 markOop mark = owner->mark();
417 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
418 // We might have encountered this object already in the case of recursive locking
419 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
420 owner->set_mark(mark->set_bias_epoch(cur_epoch));
421 }
422 }
423 }
424 }
425
426 // At this point we're done. All we have to do is potentially
427 // adjust the header of the given object to revoke its bias.
428 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL);
429 } else {
430 if (log_is_enabled(Info, biasedlocking)) {
431 ResourceMark rm;
432 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
433 }
434
435 // Disable biased locking for this data type. Not only will this
436 // cause future instances to not be biased, but existing biased
437 // instances will notice that this implicitly caused their biases
438 // to be revoked.
439 klass->set_prototype_header(markOopDesc::prototype());
440
441 // Now walk all threads' stacks and forcibly revoke the biases of
442 // any locked and biased objects of this data type we encounter.
443 for (; JavaThread *thr = jtiwh.next(); ) {
444 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
445 for (int i = 0; i < cached_monitor_info->length(); i++) {
446 MonitorInfo* mon_info = cached_monitor_info->at(i);
447 oop owner = mon_info->owner();
448 markOop mark = owner->mark();
449 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
450 revoke_bias(owner, false, true, requesting_thread, NULL);
451 }
452 }
453 }
454
455 // Must force the bias of the passed object to be forcibly revoked
456 // as well to ensure guarantees to callers
457 revoke_bias(o, false, true, requesting_thread, NULL);
458 }
459 } // ThreadsListHandle is destroyed here.
460
461 log_info(biasedlocking)("* Ending bulk revocation");
462
463 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
464
465 if (attempt_rebias_of_object &&
466 o->mark()->has_bias_pattern() &&
467 klass->prototype_header()->has_bias_pattern()) {
468 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
469 klass->prototype_header()->bias_epoch());
470 o->set_mark(new_mark);
471 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
472 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
473 }
474
475 assert(!o->mark()->has_bias_pattern() ||
476 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
477 "bug in bulk bias revocation");
478
479 return status_code;
480 }
481
482
483 static void clean_up_cached_monitor_info() {
484 // Walk the thread list clearing out the cached monitors
485 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
486 thr->set_cached_monitor_info(NULL);
487 }
488 }
489
490
491 class VM_RevokeBias : public VM_Operation {
492 protected:
493 Handle* _obj;
494 GrowableArray<Handle>* _objs;
495 JavaThread* _requesting_thread;
496 BiasedLocking::Condition _status_code;
497 traceid _biased_locker_id;
498
499 public:
500 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
501 : _obj(obj)
502 , _objs(NULL)
503 , _requesting_thread(requesting_thread)
504 , _status_code(BiasedLocking::NOT_BIASED)
505 , _biased_locker_id(0) {}
506
507 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
508 : _obj(NULL)
509 , _objs(objs)
510 , _requesting_thread(requesting_thread)
511 , _status_code(BiasedLocking::NOT_BIASED)
512 , _biased_locker_id(0) {}
513
514 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
515
516 virtual bool doit_prologue() {
517 // Verify that there is actual work to do since the callers just
518 // give us locked object(s). If we don't find any biased objects
519 // there is nothing to do and we avoid a safepoint.
520 if (_obj != NULL) {
521 markOop mark = (*_obj)()->mark();
522 if (mark->has_bias_pattern()) {
523 return true;
524 }
525 } else {
526 for ( int i = 0 ; i < _objs->length(); i++ ) {
527 markOop mark = (_objs->at(i))()->mark();
528 if (mark->has_bias_pattern()) {
529 return true;
530 }
531 }
532 }
533 return false;
534 }
535
536 virtual void doit() {
537 if (_obj != NULL) {
538 log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:");
539 JavaThread* biased_locker = NULL;
540 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker);
541 if (biased_locker != NULL) {
542 _biased_locker_id = THREAD_TRACE_ID(biased_locker);
543 }
544 clean_up_cached_monitor_info();
545 return;
546 } else {
547 log_info(biasedlocking)("Revoking bias with global safepoint:");
548 BiasedLocking::revoke_at_safepoint(_objs);
549 }
550 }
551
552 BiasedLocking::Condition status_code() const {
553 return _status_code;
554 }
555
556 traceid biased_locker() const {
557 return _biased_locker_id;
558 }
559 };
560
561
562 class VM_BulkRevokeBias : public VM_RevokeBias {
563 private:
564 bool _bulk_rebias;
565 bool _attempt_rebias_of_object;
566
567 public:
568 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
569 bool bulk_rebias,
570 bool attempt_rebias_of_object)
571 : VM_RevokeBias(obj, requesting_thread)
572 , _bulk_rebias(bulk_rebias)
573 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
574
575 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
576 virtual bool doit_prologue() { return true; }
577
578 virtual void doit() {
579 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
580 clean_up_cached_monitor_info();
581 }
582 };
583
584
585 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
586 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
587
588 // We can revoke the biases of anonymously-biased objects
589 // efficiently enough that we should not cause these revocations to
590 // update the heuristics because doing so may cause unwanted bulk
591 // revocations (which are expensive) to occur.
592 markOop mark = obj->mark();
593 if (mark->is_biased_anonymously() && !attempt_rebias) {
594 // We are probably trying to revoke the bias of this object due to
595 // an identity hash code computation. Try to revoke the bias
596 // without a safepoint. This is possible if we can successfully
597 // compare-and-exchange an unbiased header into the mark word of
598 // the object, meaning that no other thread has raced to acquire
599 // the bias of the object.
600 markOop biased_value = mark;
601 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
602 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
603 if (res_mark == biased_value) {
604 return BIAS_REVOKED;
605 }
606 } else if (mark->has_bias_pattern()) {
607 Klass* k = obj->klass();
608 markOop prototype_header = k->prototype_header();
609 if (!prototype_header->has_bias_pattern()) {
610 // This object has a stale bias from before the bulk revocation
611 // for this data type occurred. It's pointless to update the
612 // heuristics at this point so simply update the header with a
613 // CAS. If we fail this race, the object's bias has been revoked
614 // by another thread so we simply return and let the caller deal
615 // with it.
616 markOop biased_value = mark;
617 markOop res_mark = obj->cas_set_mark(prototype_header, mark);
618 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
619 return BIAS_REVOKED;
620 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
621 // The epoch of this biasing has expired indicating that the
622 // object is effectively unbiased. Depending on whether we need
623 // to rebias or revoke the bias of this object we can do it
624 // efficiently enough with a CAS that we shouldn't update the
625 // heuristics. This is normally done in the assembly code but we
626 // can reach this point due to various points in the runtime
627 // needing to revoke biases.
628 if (attempt_rebias) {
629 assert(THREAD->is_Java_thread(), "");
630 markOop biased_value = mark;
631 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
632 markOop res_mark = obj->cas_set_mark(rebiased_prototype, mark);
633 if (res_mark == biased_value) {
634 return BIAS_REVOKED_AND_REBIASED;
635 }
636 } else {
637 markOop biased_value = mark;
638 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
639 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
640 if (res_mark == biased_value) {
641 return BIAS_REVOKED;
642 }
643 }
644 }
645 }
646
647 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
648 if (heuristics == HR_NOT_BIASED) {
649 return NOT_BIASED;
650 } else if (heuristics == HR_SINGLE_REVOKE) {
651 Klass *k = obj->klass();
652 markOop prototype_header = k->prototype_header();
653 if (mark->biased_locker() == THREAD &&
654 prototype_header->bias_epoch() == mark->bias_epoch()) {
655 // A thread is trying to revoke the bias of an object biased
656 // toward it, again likely due to an identity hash code
657 // computation. We can again avoid a safepoint in this case
658 // since we are only going to walk our own stack. There are no
659 // races with revocations occurring in other threads because we
660 // reach no safepoints in the revocation path.
661 // Also check the epoch because even if threads match, another thread
662 // can come in with a CAS to steal the bias of an object that has a
663 // stale epoch.
664 ResourceMark rm;
665 log_info(biasedlocking)("Revoking bias by walking my own stack:");
666 EventBiasedLockSelfRevocation event;
667 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL);
668 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
669 assert(cond == BIAS_REVOKED, "why not?");
670 if (event.should_commit()) {
671 event.set_lockClass(k);
672 event.commit();
673 }
674 return cond;
675 } else {
676 EventBiasedLockRevocation event;
677 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
678 VMThread::execute(&revoke);
679 if (event.should_commit() && (revoke.status_code() != NOT_BIASED)) {
680 event.set_lockClass(k);
681 // Subtract 1 to match the id of events committed inside the safepoint
682 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
683 event.set_previousOwner(revoke.biased_locker());
684 event.commit();
685 }
686 return revoke.status_code();
687 }
688 }
689
690 assert((heuristics == HR_BULK_REVOKE) ||
691 (heuristics == HR_BULK_REBIAS), "?");
692 EventBiasedLockClassRevocation event;
693 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
694 (heuristics == HR_BULK_REBIAS),
695 attempt_rebias);
696 VMThread::execute(&bulk_revoke);
697 if (event.should_commit()) {
698 event.set_revokedClass(obj->klass());
699 event.set_disableBiasing((heuristics != HR_BULK_REBIAS));
700 // Subtract 1 to match the id of events committed inside the safepoint
701 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
702 event.commit();
703 }
704 return bulk_revoke.status_code();
705 }
706
707
708 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
709 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
710 if (objs->length() == 0) {
711 return;
712 }
713 VM_RevokeBias revoke(objs, JavaThread::current());
714 VMThread::execute(&revoke);
715 }
716
717
718 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
719 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
720 oop obj = h_obj();
721 HeuristicsResult heuristics = update_heuristics(obj, false);
722 if (heuristics == HR_SINGLE_REVOKE) {
723 revoke_bias(obj, false, false, NULL, NULL);
724 } else if ((heuristics == HR_BULK_REBIAS) ||
725 (heuristics == HR_BULK_REVOKE)) {
726 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
727 }
728 clean_up_cached_monitor_info();
729 }
730
731
732 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
733 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
734 int len = objs->length();
735 for (int i = 0; i < len; i++) {
736 oop obj = (objs->at(i))();
737 HeuristicsResult heuristics = update_heuristics(obj, false);
738 if (heuristics == HR_SINGLE_REVOKE) {
739 revoke_bias(obj, false, false, NULL, NULL);
740 } else if ((heuristics == HR_BULK_REBIAS) ||
741 (heuristics == HR_BULK_REVOKE)) {
742 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
743 }
744 }
745 clean_up_cached_monitor_info();
746 }
747
748
749 void BiasedLocking::preserve_marks() {
750 if (!UseBiasedLocking)
751 return;
752
753 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
754
755 assert(_preserved_oop_stack == NULL, "double initialization");
756 assert(_preserved_mark_stack == NULL, "double initialization");
757
758 // In order to reduce the number of mark words preserved during GC
759 // due to the presence of biased locking, we reinitialize most mark
760 // words to the class's prototype during GC -- even those which have
761 // a currently valid bias owner. One important situation where we
762 // must not clobber a bias is when a biased object is currently
763 // locked. To handle this case we iterate over the currently-locked
764 // monitors in a prepass and, if they are biased, preserve their
765 // mark words here. This should be a relatively small set of objects
766 // especially compared to the number of objects in the heap.
767 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
768 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
769
770 ResourceMark rm;
771 Thread* cur = Thread::current();
772 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
773 if (thread->has_last_Java_frame()) {
774 RegisterMap rm(thread);
775 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
776 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
777 if (monitors != NULL) {
778 int len = monitors->length();
779 // Walk monitors youngest to oldest
780 for (int i = len - 1; i >= 0; i--) {
781 MonitorInfo* mon_info = monitors->at(i);
782 if (mon_info->owner_is_scalar_replaced()) continue;
783 oop owner = mon_info->owner();
784 if (owner != NULL) {
785 markOop mark = owner->mark();
786 if (mark->has_bias_pattern()) {
787 _preserved_oop_stack->push(Handle(cur, owner));
788 _preserved_mark_stack->push(mark);
789 }
790 }
791 }
792 }
793 }
794 }
795 }
796 }
797
798
799 void BiasedLocking::restore_marks() {
800 if (!UseBiasedLocking)
801 return;
802
803 assert(_preserved_oop_stack != NULL, "double free");
804 assert(_preserved_mark_stack != NULL, "double free");
805
806 int len = _preserved_oop_stack->length();
807 for (int i = 0; i < len; i++) {
808 Handle owner = _preserved_oop_stack->at(i);
809 markOop mark = _preserved_mark_stack->at(i);
810 owner->set_mark(mark);
811 }
812
813 delete _preserved_oop_stack;
814 _preserved_oop_stack = NULL;
815 delete _preserved_mark_stack;
816 _preserved_mark_stack = NULL;
817 }
818
819
820 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
821 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
822 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
823 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
824 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
825 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
826 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
827
828
829 // BiasedLockingCounters
830
831 int BiasedLockingCounters::slow_path_entry_count() {
832 if (_slow_path_entry_count != 0) {
833 return _slow_path_entry_count;
834 }
835 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
836 _rebiased_lock_entry_count + _revoked_lock_entry_count +
837 _fast_path_entry_count;
838
839 return _total_entry_count - sum;
840 }
841
842 void BiasedLockingCounters::print_on(outputStream* st) {
843 tty->print_cr("# total entries: %d", _total_entry_count);
844 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
845 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
846 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
847 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
848 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
849 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
850 }